Method of fabricating a laminate and product thereof

ABSTRACT

A method of manufacturing an electrical coil comprising providing an electrically conductive strip which is superposed and adhesively secured to a dielectric web having nonplanar portions intermediate the adhesive and the transverse edges of the dielectric web. Effecting transverse expansion of the dielectric web to a width greater than the conductive strip by compressing the laminated strip. An alternate laminate structure wherein some or all of the nonplanar dielectric web portions are loosely bonded to the conductive strip in such a fashion as to permit transverse expansion of the dielectric web responsive to application of a compressive force. In one form of the invention, the laminated conductive strip is wound into coil form under sufficient winding tension to cause sequential application of compressive force to successive wraps of said coil in order to transversely expand the dielectric web. The dielectric web serves to insulate edges of adjacent conductive wraps of the coil. Establishing a multiple width laminate of the conductive strip and subsequently longitudinally slitting the multiple width laminate into a number of individual laminated strips. An electrical conductor-dielectric laminate having an elongated electrically conductive strip and a dielectric web adhesively secured to the conductive strip. The adhesive securing the conductive strip to the dielectric is spaced inwardly from the transverse edges of the dielectric web. The dielectric web has nonplanar portions between the adhesive and the transverse edges to provide a restricted width. The dielectric web has a restricted width generally equal to the width of the conductive strip and an expanded width greater than the width of the conductive strip. An electrical coil wound from the electrical conductor-dielectric laminate having the expanded width dielectric web serving as an electrical insulator between adjacent conductive wraps of the coil.

March 12, 1974: L... M. BUTCHER 3,796,621

METHOD OF FABRICAT'ING A LAMINATE AND PRODUCT THEREOF Original Filed Sept. 10, 1971 2 Sheets-Sheet 1 FIG. I

l\\ X\\\ X\\\ 2 mew/06a mza/oaa'mzalo March 12, 1974 L. M. BUTCHER METHOD OF FABRICATING A LAMINATE AND PRODUCT THEREOF Original Filed Sept. 10, 19*71 FIG. 4.

2 Sheets-Sheet 2 United States Patent 3,796,621 METHOD OF FABRICATING A LAMINATE AND PRODUCT THEREOF Louis M. Butcher, New Kensington, Pa., assignor to Aluminum Company of America, Pittsburgh, Pa.

Original application Sept. 10, 1971, Ser. No. 179,288, now Patent No. 3,727,163. Divided and this application Apr. 21, 1972, Ser. No. 246,488

Int. Cl. B31c 13/00; H01g 13/00 US. Cl. 156-192 Claims ABSTRACT OF THE DISCLOSURE A method of manufacturing an electrical coil comprising providing an electrically conductive strip which 1s superposed and adhesively secured to a dielectric web having nonplanar portions intermediate the adhesive and the transverse edges of the dielectric web. Effecting transverse expansion of the dielectric web to a width greater than the conductive strip by compressing the laminated strip. An alternate laminate structure wherein some or all of the nonplanar dielectric web portions are loosely bonded to the conductive strip in such a fashion as to permit transverse expansion of the dielectric web responsive to application of a compressive force. In one form of the invention, the laminated conductive strip is wound into coil form under suflicient winding tension to cause sequential application of compressive force to successive wraps of said coil in order to transversely expand the dielectric web. The dielectric web serves to insulate edges of adjacent conductive Wraps 0f the coil. Establishing a multiple width laminate of the conductive strip and subsequently longitudinally slitting the multiple width laminate into a number of individual laminated strips.

An electrical conductor-dielectric laminate having an elongated electrically conductive strip and a dielectric web adhesively secured to the conductive strip. The adhesive securing the conductive strip to the dielectric is spaced inwardly from the transverse edges of the dielectric web. The dielectric web has nonplanar portions between the adhesive and the transverse edges to provide a restricted width. The dielectric Web has a restricted width generally equal to the Width of the conductive strip and an expanded width greater than the width of the conductive strip.

Anelectrical coil wound from the electrical conductordielectric laminate having the expanded width dielectric web serving as an electrical insulator between adjacent conductive wraps of the coil.

This is a division of application Ser. No. 179,288, filed Sept. 10, 1971, now US. Pat. 3,727,163.

BACKGROUND OF THE INVENTION Field of the invention This invention relates generally to a method of manufacturing a laminated strip for use in electrical coils and, more specifically, it relates to the use of such strip in methods of automatically providing electrical insulation between adjacent conductive wraps so as to prevent undesired edge to edge shorting.

Description of the prior art It has been known to manufacture electrical coils by employing conductive strip materials wrapped in coil form with insulating materials interposed between adjacent wraps. Such coils are frequently used in capacitors, solenoids, transformers and the like. One of the difiiculties encountered in manufacturing such electrical coils has been the need to provide insulating material of greater width than the conductive strip intermediate successive conductive wraps in order to prevent undesired edge to 3,796,621 Patented Mar. 12, 1974 edge shorting. In the event that the dielectric webs were prelaminated to the conductor sheet prior to slitting into individual widths, both plies would have an identical width and effective insulating against undesired edge to edge shorting would not be provided. As a result it is necessary to use a wider dielectric web which has been separately fabricated. It has generally been the practice to manufacture such coils by first slitting the conductor to the desired final width and subsequently, during the actual coil winding, interleaving or inserting the wider dielectric in order to provide effective insulation against edge to edge shorting. This requires not only burdensome independent handling and feeding of the conductor and dielectric, but also requires aligning of the independent strips and coordination of feed rates. In addition, tensile fracture of the unsupported conductive strip during application of winding tensions caused disruptive and inefficient Work stoppages.

It has also been known to slit the conductor sheet into individual widths and to subsequently bond a wider dielec trio thereto prior to coil winding.

It, therefore, has been necessary, in this type of coil manufacture, to employ inefficient methods involving first providing the individual width conductive strips and subsequently providing the wider dielectric for each such strip in a separate stage of manufacture of the coil, either through interleaving during winding or lamination of an independent dielectric strip of greater width prior to winding. See generally U.S. Pats. 3,303,550 and 3,477,126.

There remains, therefore, a need for an eifective means of coil fabrication which provides the desired electrical insulating characteristics and yet does not require ineflicient, separate creation, handling and interleaving of the dielectric material.

SUMMARY OF THE INVENTION The above described need has been fulfilled by the method of this invention and the product created thereby. In the method of this invention an electrically conductive strip, which will generally be metal foil or sheet, is superposed and adhesively secured to a dielectric web. The adhesive is so positioned and the dielectric is so configurated as to provide nonplanar portions of the dielectric disposed intermediate the adhesive and the trans-verse edges of the dielectric web. In an alternate form, some or all of the nonplanar portions are loosely bonded to the conductive strip in such a fashion as to permit transverse expansion responsive to application of a compressive force. In this restricted width position the dielectric and the conductive strip have generally identical transverse widths. The laminate is then placed in compression in order to effect a transverse expansion of the dielectric web to an expanded width which is greater than the width of the conductive strip. This may conveniently be accomplished during winding of the coils with the winding tension so established as to result in automatic sequential application of compressive force to successive laminate wraps to create transverse expansion of the dielectric web by reforming of some or all the nonplanar portions.

This method also contemplates the use of multiple width laminates having a dielectric web and conductive strip joined by bonding the strip and web longitudinally at a number of transversely spaced positions. The dielectrio web is provided with nonplanar portions in regions intermediate the adhesive sectors. The multiple width laminate may then be slit into a number of individual lam inated strips each having an adhesive sector disposed at a position spaced inwardly from the transverse edges of the dielectric web with each web having a restricted width substantially equal to the width of the conductive strip.

Subsequently applied compressive force results in the desired transverse expansion of the dielectric web.

The method of this invention produces an electrical conductor-dielectric laminate having an elongated electrically conductive strip and a dielectric web adhesively secured to the conductive strip by means of an adhesive which is spaced inwardly from the transverse edges of the dielectric web. The nonplanar portions of the dielectric Web provide a restricted width which, in effect, creates a reservoir of material for transverse expansion when the longitudinal strip is placed in compression. This compressive force may conveniently be applied either during winding of the electrical coil or by an independent operation.

A laminated electrical coil produced by this invention has a conductive strip which is adhesively secured to a wider dielectric web which projects transversely beyond both edges of the conductive strip. This establishes effective insulation against edge to edge shorting. The adhesive is preferably substantially continuous and is provided in a generally longitudinally oriented sector disposed subtantially centrally with respect to the conductive strip. The dielectric web preferably has an expanded width of 3 to 25% greater than the width of the conductive strip. The amount of excess width is preferably related to contemplated electrical potential with respect to which the coil will be exposed, with increased width being employed with increased electrical potential in order to improve insulating characteristics.

It is an object of this invention to provide a method of simply and effectively producing a laminated electrical coil employing a conductive strip and a wider dielectric web which effectively insulates edges of adjacent conductive wraps of the electrical coil.

It is another object of this invention to provide such a method wherein the laminate may be produced with both plies of generally equal width and subsequent tensioning of the laminate during rewinding effectively sequentially compressing adjacent coil wraps to expand the dielectric web.

It is another object of this invention to provide such a method wherein the laminate may be prepared initially in multiple width dimension and subsequently slit in the normal fashion to provide a number of laminate strips which are adapted to be altered during the application of normal coil winding tension in order to provide effective insulation of the edges of adjacent conductive wraps.

It is another object of this invention to produce a conductive metal strip laminate and the resultant insulated coil in such a fashion as to make maximum use of conventional equipment while eliminating the need for separate handling and insertion or joinder of an insulating web.

These and other objects of the invention will be more fully understood from the following description of the invention, on reference to the illustrations appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view, partially broken away, showing a form of nonplanar dielectric material contemplated by this invention.

FIG. 2 is a perspective view, partially broken away, showing one form of laminate of this invention during the process of slitting a multiple width member into individual laminate strips.

FIG. 3 illustrates an electrical coil of this invention having the adhesively bonded dielectric projecting trans versely outwardly.

FIG. 4 is a sectional view taken through 4-4 of FIG. 3 showing the insulation of adjacent conductive wraps of the coil.

FIG. 5 shows a modified form of dielectric web contemplated by this invention.

4 FIG. 6 is a cross sectional illustration taken through 6-6 of FIG. 5 and shows nonplanar portions of the dielectric web.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now more specifically to FIG. 1, there is shown a dielectric web 2 which has a leading end 4 and a pair of transverse edges 6, 8. It is noted that the dielectric web 2 has a plurality of undulating sections 10 which are transversely directed and define a plurality of longitudinal grooves 12. These undulating sections 10 provide a reservoir of material in the restricted width dielectric web 2 which facilitate transverse expansion to an enlarged width in a manner which will be described in detail below. While for convenience of illustration reference herein will be made to a dielectric web 2 having undulating sections 10, it will be appreciated that various forms of profile which provide for subsequent transverse expansion of restricted portions of the dielectric web 2 may be employed. The term nonplanar portions, and words of similar import, as used herein shall refer to departures from a generally planar, flat web profile, which departures reduce the transverse width of the web and provide a reservoir of material which facilitates subsequent trans-verse expansion of the web to an enlarged width. In general, the expression will contemplate changes in direction of the web as it extends in a transverse direction and include bends or folds which have at least a component extending in a transverse direction, but will not contemplate mere variations in web thickness.

Referring now to FIG. 2, there is shown a multiwidth laminate of this invention. The laminate has an undulating dielectric web 2 which is secured to a superposed electrically conductive metal strip 16, which is generally of foil or sheet thickness. The dielectric web 2 is adhesively bonded to the metal strip 16 by means of a number of adhesive sections 18 which are generally longitudinally directed and transversely spaced with respect to each other. The adhesive sections 18 are preferably, but not necessarily, longitudinally substantially continuous.

In a preferred form of this invention the metal strip 16 will be an electrically conductive strip having a thickness of about 0.00014 inch to 0.010 inch. The smaller gauges are generally preferred for end uses such as eapacitor coils, while the larger gauges are generally preferred for heavy duty transfomers and the like. While numeous strip materials may be employed, aluminum and copper are among the preferred materials because they are highly conductive and relatively inexpensive.

With respect to the dielectric web 2 one of the preferred materials is paper, such as impregnated natural kraft having a thickness of about 0.0003 to 0.005 inch. Also uniquely suited for use with this invention are a wide range of plastic films including polyethylene, polyester, vinyl, polyvinyl chloride and polycarbonate having a thickness of about 0.00015 to 0.005 inch. The dielectric Web 2 shown in FIGS. 1 and 2 may be a plastic material which has been provided with undulations in any convenient manner, such as by extrusion and/or formation between a pair of mated roller dies.

With respect to adhesives, any adhesive which will effectively bond the two materials at the desired predetermined locations and will not deteriorate under winding tensions and exposure to a wide range of atmospheric conditions is suitable. Typical of suitable materials are thermoplastics, such as polyurethane, vinyl-s, polyesters, polyamides and epoxides. Hot melt adhesives such as parafiin waxes, microcrystalline waxes, natural waxes and asphalt and coal based products may also be employed. Also suitable for use with certain dielectric materials are water based adhesives such as casein neoprenes, latexes, styrene butadiene rubber and polyvinylacetates.

While it is important to establish the laminate of this invention by bonding the conductive strip to the dielectric web in the manner described herein, it will be appreciated that with some combinations of materials this may be accomplished by direct bonding of one material to the other without the use of an independent adhesive. For simplicity of description the terms adhesively secured, adhesively bonded and words of similar import shall be deemed to include both bonding by means of an independent adhesive and by self-bonding without the use of a separate adhesive material. Also, while reference will generally be made herein to a bond between the dielectric web and conductive strip, it will be appreciated that a number of bonded regions may be provided so long as the freedom of transverse expansion through displacement of nonplanar portions of the dielectric web is preserved.

Referring once again to FIG. 2, it is seen that the multiple width metal strip 16 is longitudinally severed at a number of locations by means of slitters 20 in order to establish a number of individual laminated strips having metal strips 16a to which are secured a number of dielectric webs 2a. It is noted that the adhesive is preferably applied generally transversely centrally of each individual metal strip 16a. The adhesive preferably covers less than about two-thirds of the surface area of the surface of the metal strip 16a to which web 2a is secured. This results'in the restricted width dielectric W-eb 2a having a substantially equal width to the individual metal strip 16a. This restricted width is provided by nonplanar portions in the form of undulating surfaces disposed intermediate the adhesive section 18 and the transverse edges 8, 6. Division by means of slitters 2.0 is eifected at positions generally midway between adjacent adhesive sections 18. While the preferred form of this embodiment of the invention contemplates the use of generally centrally disposed substantially continuous adhesive sections 18, it will be appreciated that the invention is not so limited. Longitudinally discontinuous sections, for example, may be employed. Other patterns of adhesive which elfectively secure the dielectric 2a to a metal strip 16a in such a fashion as to provide a strong, durable bond while establishing a restricted width dielectric web 2a with nonplanar portions being free to expand in a transverse direction in order to create an increased width may be employed.

An individual laminated strip of the type shown is subjected to compressive forces applied generally to exposed surfaces of the dielectric web 2a and metal strip 16a. As used herein, reference to compressive force or compression and words of similar import as applied to the laminate shall refer to compressive force applied to 0p posed exposed surfaces of the laminate in such a fashion as to create compression and transverse expansion of nonplanar portions of the dielectric Web. This is preferably accomplished by leveling i.e., reduction of the height of nonplanar portions of the dielectric web to produce a generally planar dielectric layer without appreciably reducing the web thickness through thinning of the material, as opposed to changes in direction of the web as it extends in a transverse direction. This compressively established transverse expansion serves to effect the desired expansion of the dielectric web 2a from its initial restricted width to an enlarged width which is greater than the width of metal strip 16a without impairing the basic web strength. In general, it will be preferred for purposes of subsequent eifective coil formation to have the transverse expansion effected in both transverse directions. One advantage of the present invention is that it not only elrninates the need for a separate step in coil fabrication involving the insertion of a dielectric, but also the desired transverse expansion may be effected by means of tension established during normal coil winding procedures. This tension creates compression of each coil wrap sequentially to expand the dielectric. As a result, one using the above described method need not establish any special procedures for handling the material of this invention or winding of coils therefrom. In fact, the use of the laminated strip of this invention reduces the likelihood of strip fracture during winding as a result of winding tension as compared with winding unbacked strip which is being interleaved with a dielectric during winding. Also, the lamnate of this invention reduces the burden of obtaining proper alignment between the conductive strip and a separate dielectric during interleaving of the dielectric with successive wraps of a conductive strip.

In lieu of establishing transverse expansion of the dielectric web responsive to compressive forces established by winding tension created during coil formation, one might establish the transverse Widening by an independent compressing operation, as by passing the laminated strip through a pair of mated rolls to establish compression. Also, rewinding the slit laminate strip, independent of and prior to coil formation, may be employed, if desired. The former approach is generally the most expeditious means of effecting expansion of the dielectric as it eliminates the need for independent processing steps.

Referring'now to FIGS. 3 and 4, an electrical coil made by the method of this invention is illustrated. FIG. 3 shows a coil 22 having a plurality of Wraps of the laminate consisting of a conductive metal strip 24 and a dielectric web 26. The outer ply 28 may be secured in place by a suitable retaining element (not shown). As is seen in the detailed illustration of FIG. 4, the dielectric web 26 has been secured to the metal strip 24 by means of an adhesive 30. It is noted that, as is preferred, the adhesive is generally centrally disposed and is spaced transversely inwardly from the edges of the expanded width dielectric web 26. It is seen that the width of the expanded dielectric web 26 exceeds the width of the metal strip 24 and projects transversely outwardly beyond each edge 32, 34 of the metal strip 24. This distance is suflicient to provide electrical insulation between adjacent wraps of the metal strip 24 so as to prevent undesired edge to edge shorting. In the preferred form, the expanded dielectric Web 26 will have a width of about 3 to 25% greater than the Width of the metal strip 24.

Referring now to FIGS. 5 and 6, another form of dielectric web contemplated by this invention will be con-,- sidered. This form of dielectric Web is a crepe paper which may be formed in the conventional fashion. The dielectric web shown in FIGS. 5 and 6 is generally unsymmetrical. It has random orientation of the nonplanar portions provided by a multiplicity of folds 36 having various orientations, depths and lengths. The profile of a sampling of these folds 36 is shown in FIG. 6. This type of dielectric web is employed in the same fashion as the above described dielectric web in that it is adhesively bonded to a superposed conductor strip in such a fashion as to provide nonplanar portions in the space intermediate the adhesive and the transverse edges 38, 40. In a preferred use of this dielectric Web, the web will have adhesive bonding provided in the region A and will have unbonded sectors B, C. It is preferred that the region A be less than two-thirds of the transverse width of the conductor strip to which the dielectric web will be secured.

EXAMPLE In order to illustrate the manner in which the present invention may be employed, an example will be considered. An aluminum foil material having a thickness of about 0.002 and a width of about 30 inches is coated with 28 continuous longitudinal ribbons by any convenient means such as gravure rolls. These ribbons of adhesive are spaced about one inch from each other with the transverse outermost ribbons being spaced about onehalf inch from the edges of the foil material. An impregnated natural kraft paper having a thickness of about 0.0005 inch is provided with nonplanar portions establishing a restricted width of about 30 inches and is laminated to the aluminum foil by means of the adhesive. The laminated material is subsequently slit longitudinally to provide a number of elongated laminated strips one inch wide having the adhesive joinder effected generally centrally and unbonded regions on alternate sides of the adhesively bonded portions. The individual laminated strips are then subjected to winding tension either in placing them on rewind reels or in winding them into the ultimate coil structure. The winding tension creates compressive force on each wrap of the laminate as it is wound on the coil. This produces a transverse expansion of the dielectric web in both directions in order to establish the desired expanded width for the dielectric.

In the embodiments of the invention described above freedom of transverse expansion through deformation of the dielectric web has been preserved by providing effective bonding of the dielectric web to the conductive strip, while preserving unbonded nonplanar portions intermediate the bonded section and the transverse edges of the dielectric. In another embodiment of this invention the laminate may be established with loose bonds between the dielectric web and conductive strip with bonding being effected between substantially all nonplanar portions of the dielectric web and the conductive strip. The term loose bond and words of similar import as used herein shall refer to adhesive or self-bonded joinder of the dielectric web to the conductive strip in such a fashion as to permit transverse expansion of some or all of the nonplanar portions of the dielectric web responsive to application of a compressive force to the laminate. While such loose bonds may be provided in the central transverse portions of the laminate and/or in the transversely outwardly disposed nonplanar portions, it is preferred to provide such loose bonds substantially continuously across the width of the laminate, with or without longitudinal continuity. As the nonplanar portions of the dielectric web will bring portions of the web out of contact with the conductive strip, the term continuous as used in this context shall refer to bonding between those portions of the dielectric which are initially in surface to surface contact with the conductive strip and will not require bonding of those portions which are not in such contact. When the bond is effected across the entire width of the laminate in this fashion, it will be deemed to be transversely continuously bonded regardless of the presence or absence of longitudinal continuity of the bond.

The use of continuous adhesive advantageously eliminates the need for special patterned adhesive applicators and/or bonding apparatus. Also, the need for predetermined strip widths which result in proper positioning of ribbons of adhesive with respect to transverse strip edges is eliminated. Thus, multiwidth preparation of the laminate and subsequent slitting is easier to accomplish. In this fashion one may employ full adhesive coating and have greater flexibility of slitting practices, while retaining the benefits of this invention.

Loose bonds between the dielectric web and the conductive strip may be obtained by the use of hot melt adhesives such as microcrystalline wax or other asphalt or coal tar based adhesives. In addition, pressure sensitive adhesives may be employed to obtain efi ective joinder of the two laminate plies while preserving the desired freedom of transverse expansion. In addition to the use of various other types of adhesives, use of the dielectric web to provide a self-adhered bond may be employed.

Transverse expansion of dielectric portions of laminates effected by loose bonding is obtained in essentially the same fashion as with other embodiments of this invention.

In effecting transverse expansion of the dielectric web of laminates of this invention compressive force is applied to the laminate. This force may be considered as being applied to a horizontally oriented laminate, for example, by vertical forces applied in a relative closing direction to exposed upper and lower surfaces of the laminate. This will produce an unfolding or transverse expansion of the restricted width dielectric web. In a preferred form, this expansion is obtained during laminate winding as a result of the longitudinal winding tension causing each succeeding wrap of the laminate to exert a compressive force on the previous Wrap to flatten the nonplanar portions and transversely enlarge the restricted width dielectric web to the desired expanded width. The tension which must be applied in order to establish the desired expansion is a function of the amount of transverse expansion desired and the extent to which the nonpolar portions depart from the general plane of the dielectric web. The tension applied cannot be more than the ultimate tensile strength of the laminate. There is no absolute minimum tension required as it has been found that conventional winding tensions are more than adequate to establish sufficient compressive force to effect a minimum desired transverse expansion of the dielectric to prevent undesired edge to edge shorts. In general, it is preferred to provide a minimum tension of about /2 pound per mil inch of width of dielectric web. The term mil inc refers to the thickness of the dielectric web in the mils multiplied by the width of the dielectric web in inches.

It will, therefore, be appreciated that the method and resultant product of this invention produce a means of effectively establishing a laminated material wherein the conductive strip has a first width and an adhesively bonded superposed dielectric web has an expanded width greater than that of the conductive metal strip. This is accomplished without the need for a separate operation which either laminates a wider dielectric strip to the conductive strip or requires interleaving of a dielectric material. All of this is accomplished by providing a laminate which has certain portions of the conductive strip bonded to a dielectric Web. The dielectric web has nonplanar portions, at least in the regions intermediate the adhesive and the transverse edges of the dielectric. In another form of the invention, a loose bond permits a substantially continuous bond between the dielectric web and conductive strip. The transverse expansion may economically be effected by application of a compressive force either as a separate operation or during normal winding procedures in an automatic fashion and may preferably be accomplished during electrical coil winding.

While for purposes of simplicity of illustration the conductive strip has been shown as being disposed above a generally horizontal underlying dielectric web, it will be appreciated that relative orientations of the laminate plies during securement and force application are illustrative and all that is required is that the strip and web be secured in the desired position of generally surface to surface superposed adjacency, without regard to orientation of the laminate or which material overlies the other during laminate formation and force application.

Whereas particular embodiments of the invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details may be made without departing from the invention as defined in the appended claims.

What is claimed is: 1. A method of manufacturing an electrical coil comprising providing a laminate of an electrically conductive strip adhesively bonded to a dielectric web having nonplanar portions,

effecting transverse expansion of said dielectric web by placing said laminate in compression to establish an expanded dielectric web width greater than said conductive strip, and

effecting said transverse expansion by leveling said nonplanar portions of said dielectric web to produce a generally planar dielectric layer.

2. The method of claim 1 including providing said laminate with at least one loose bon securing said conductive strip to said dielectric web, and

modifying said loose bond by compressively reforming said laminate to effect transverse expansion of said dielectric web to an expanded width greater than said conductive strip.

3. A method of manufacturing an electrical coil comprising providing a laminate of an electrically conductive strip adhesively bonded to a dielectric web having nonplanar portions,

providing said dielectric Web with nonplanar portions disposed intermediate said adhesive bond and the transverse edges of said dielectric web,

effecting transverse expansion of said dielectric web by placing said laminate in compression to establish an expanded dielectric web width greater than the transverse width of said conductive strip,

effecting said transverse expansion by leveling said nonplanar portions of said dielectric web to produce a generally planar dielectric layer, and

effecting said transverse expansion during winding of said laminate by establishing said compression sequentially as a reslt of tensile forces established in said laminate during winding.

4. The method of claim 3 including establishing a multiple width laminate of said conductive strip and dielectric web by bonding said strip and said web longitudinally at a number of transversely spaced positions,

slitting said multiple width laminate into a number of individual laminates each having said web and said strip adhesively secured at a position spaced inwardly from the transverse edges of said laminate, and

subsequently effecting said transverse expansion of said dielectric web by applying compressive forces to said laminates.

5. The method of claim 4 including subsequent to effecting slitting to establish .said individual laminates and efiecting said transverse expansion of said dielectric webs, rewinding said individual laminates to establish coils having said dielectric webs electrically insulating edges of adjacent conduc tive wraps of said coils.

References Cited UNITED STATES PATENTS 3,505,159 4/ 1970 Winter 156229 X 3,477,126 11/1969 Price 156-299 X 3,589,975 r 6/1971 Andrews et a1. 156244 3,159,516 12/1964 Harris 156-292 X 3,378,626 4/1968 Tucker 29605 3,596,213 7/1971 England 3l7260 RALPH S. KENDALL, Primary Examiner B. J. LEWRIS, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,796,621. Dated March 12, 1974 Inventor(s) Louis M. Butcher It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 4, line 70 After "and" change 7 "epoxides" to -epoxies--.

Col. 6, line 8 After "the?" change "lamnate" to -laminate--.

Col. 8, lines 11 & l2 7 After "the" change 5 "nonpolar" to -nonp1anar-.

Signed and sealed this 9th day of July 1974.

(SEAL) Attest:

McCOY M. GIBSON, JR. C. MARSHALL DA'NN Attesting Officer Commissioner of Patents UsCOMM-DC 60376-P69 u.s. GOVERNMENT rmu'rms ornc: Ian o-au-su, 

